Silica-filled elastomeric compounds

ABSTRACT

The present invention provides a composition comprising at least one halobutyl elastomer, at least one mineral filler and at least one protected thiol modifier. In another aspect the present invention provides a process which comprises mixing a halobutyl elastomer with at least one mineral filler, in the presence of at least one protected thiol modifier, and curing the resulting filled halobutyl elastomer.

FIELD OF THE INVENTION

The present invention relates to silica-filled halogenated butylelastomers, in particular bromobutyl elastomers (BIIR).

BACKGROUND OF THE INVENTION

It is known that reinforcing fillers such as carbon black and silicagreatly improve the strength and fatigue properties of elastomericcompounds. It is also known that chemical interaction occurs between theelastomer and the filler. For example, good interaction between filler,in particular carbon black and highly unsaturated elastomers such aspolybutadiene (BR) and styrene butadiene copolymers (SBR) occurs becauseof the large number of carbon-carbon double bonds present in thesecopolymers. Butyl elastomers are known to interact poorly with fillerslike carbon black. For example, a compound prepared by mixing carbonblack with a combination of BR and butyl elastomers results in domainsof BR, which contain most of the carbon black, and butyl domains-whichcontain very little carbon black. It is also known that butyl compoundshave poor abrasion resistance.

WO-99/09036-A1 discloses protected thiol modifiers in general and alsotheir use in silica filled compound comprising organic polymers.However, this reference is silent about the beneficial use of protectedthiol modifiers in compounds comprising halogenated butyl rubbers. Butylelastomers may have only one tenth, or fewer, of the carbon-carbondouble bonds found in BR or SBR as disclosed in WO-99/09036-A1. Thus,our findings that the use of protected thiol modifiers in fact resultsin compounds with a very good balance of physical properties while stillmaintaining acceptable levels of processability is surprising.

SUMMARY OF THE INVENTION

The present invention provides a composition comprising at least onehalobutyl elastomer, at least one mineral filler and at least oneprotected thiol modifier.

It has been discovered that protected thiol modifiers enhance theinteraction of halobutyl elastomers with mineral fillers, resulting inimproved compound properties such as tensile strength and abrasionresistance (DIN). This is surprising as the non-halogenated butylelastomer does not respond in the same way.

Accordingly, in another aspect the present invention provides a processwhich comprises mixing a halobutyl elastomer with at least one mineralfiller, in the presence of at least one protected thiol modifier, andcuring the resulting filled halobutyl elastomer.

The halobutyl elastomer that is admixed with one protected thiolmodifier may be a mixture with another elastomer or elastomericcompound. The halobutyl elastomer should constitute more than 5% of anysuch mixture. Preferably the halobutyl elastomer should constitute atleast 10% of any such mixture. In some cases it is, preferred not to usemixtures but to use the halobutyl elastomer as the sole elastomer. Ifmixtures are to be used, however, then the other elastomer may be, forexample, natural rubber, polybutadiene, styrene-butadiene orpoly-chloroprene or an elastomer compound containing one or more ofthese elastomers.

The filled halobutyl elastomer can be cured in the presence of at leastone cross-linking agent to obtain a product which has improvedproperties, for instance in abrasion resistance, rolling resistance andtraction. Curing can be effected with sulfur but does not have to be.The preferred amount of sulfur is in the range of from 0 to 2.0 parts byweight per hundred parts of rubber. An activator, for example zincoxide, may also be used, in an amount in the range of from 0.5 parts to2 parts by weight. Other ingredients, for instance stearic acid,antioxidants, or accelerators may also be added to the elastomer priorto curing. Sulphur curing is then effected in the known manner. See, forinstance, chapter 2, “The Compounding and Vulcanization of Rubber”, of“Rubber Technology”, 3^(rd) edition, published by Chapman & Hall, 1995,the disclosure of which is incorporated by reference.

Other curatives known to cure halobutyl elastomers may also be used. Anumber of compounds are known to cure halobutyl elastomers, for example,such as bis dieneophiles (for example m-phenyl-bis-maleimide, HVA2),phenolic resins, amines, amino-acids, peroxides, zinc oxide and thelike. Combinations of the aforementioned curatives may also be used.

The mineral-filled halobutyl elastomer of the invention can be admixedwith other elastomers or elastomeric compounds before it is subjected tocuring.

DETAILED DESCRIPTION OF THE INVENTION

The phrase “halobutyl elastomer(s)” as used herein refers to achlorinated or brominated butyl elastomer. Brominated butyl elastomersare preferred, and the invention is illustrated, by way of example, withreference to such bromobutyl elastomers. It should be understood,however, that the invention extends to the use of chlorinated butylelastomers.

Thus, halobutyl elastomers suitable for use in the practice of thisinvention include, but are not limited to, brominated butyl elastomers.Such elastomers may be obtained by bromination of butyl rubber (which isa copolymer of isobutylene and a co-monomer that is usually a C₄ to C₆conjugated diolefin, preferably isoprene—(brominatedisobutene-isoprene-copolymers BIIR)). Co-monomers other than conjugateddiolefins can be used, however, and mention is made of alkyl-substitutedvinyl aromatic co-monomers such as C₁-C₄-alkyl substituted styrene. Anexample of such an elastomer which is commercially available isbrominated isobutylene methylstyrene copolymer (BIMS) in which theco-monomer is p-methylstyrene.

Brominated butyl elastomers typically comprise in the range of from 0.1to 10 weight percent of repeating units derived from isoprene and in therange of from 90 to 99.9 weight percent of repeating units derived fromisobutylene (based upon the hydrocarbon content of the polymer) and inthe range of from 0.1 to 9 weight percent bromine (based upon thebromobutyl polymer). A typical bromobutyl polymer has a molecularweight, expressed as the Mooney viscosity according to DIN 53 523 (ML1+8 at 125° C.), in the range of from 25 to 60.

For use in the present invention the brominated butyl elastomerpreferably contains in the range of from 0.5 to 5 weight percent ofrepeating units derived from isoprene and in the range of from 95 to99.5 weight percent of repeating units derived from isobutylene (basedupon the hydrocarbon content of the polymer) and in the range of from0.2 to 3 weight percent, preferably from 0.75 to 2.3 weight percent, ofbromine (based upon the brominated butyl polymer).

A stabilizer may be added to the brominated butyl elastomer. Suitablestabilizers include calcium stearate and epoxidized soy bean oil,preferably used in an amount in the range of from 0.5 to 5 parts byweight per 100 parts by weight of the brominated butyl rubber (phr).

Examples of suitable brominated butyl elastomers include BayerBromobutyl® 2030, Bayer Bromobutyl® 2040 (BB2040), and Bayer Bromobutyl®X2 commercially available from Bayer. Bayer BB2040 has a Mooneyviscosity (ML 1+8@125° C.) of 39±4, a bromine content of 2.0±0.3 wt %and an approximate molecular weight of 500,000 grams per mole.

The brominated butyl elastomer used in this invention may also be agraft copolymer of a brominated butyl rubber and a polymer based upon aconjugated diolefin monomer. Our co-pending Canadian Patent Application2,279,085 is directed towards a process for preparing such graftcopolymers by mixing solid brominated butyl rubber with a solid polymerbased on a conjugated diolefin monomer which also includes someC—S—(S)_(n)—C bonds, where n is an integer from 1 to 7, the mixing beingcarried out at a temperature greater than 50° C. and for a timesufficient to cause grafting. The disclosure of this application isincorporated herein by reference. The bromobutyl elastomer of the graftcopolymer can be any of those described above. The conjugated diolefinsthat can be incorporated in the graft copolymer generally have thestructural formula:

wherein R is a hydrogen atom or an alkyl group containing from 1 to 8carbon atoms and wherein R₁ and R₁₁ can be the same or different and areselected from the group consisting of hydrogen atoms and alkyl groupscontaining from 1 to 4 carbon atoms. Some representative non-limitingexamples of suitable conjugated diolefins include 1,3-butadiene,isoprene, 2-methyl-1,3-pentadiene, 4-butyl-1,3-pentadiene,2,3-dimethyl-1,3-pentadiene 1,3-hexadiene, 1,3-octadiene,2,3-dibutyl-1,3-pentadiene, 2-ethyl-1,3-pentadiene,2-ethyl-1,3-butadiene and the like. Conjugated diolefin monomerscontaining from 4 to 8 carbon atoms are preferred, 1,3-butadiene andisoprene being especially preferred.

The polymer based on a conjugated diene monomer can be a homopolymer, ora copolymer of two or more conjugated diene monomers, or a copolymerwith a vinyl aromatic monomer.

The vinyl aromatic monomers which can optionally be used are selected soas to be copolymerizable with the conjugated diolefin monomers beingemployed. Generally, any vinyl aromatic monomer which is known topolymerize with organo-alkali metal initiators can be used. Such vinylaromatic monomers usually contain in the range of from 8 to 20 carbonatoms, preferably from 8 to 14 carbon atoms. Some examples of vinylaromatic monomers which can be so copolymerized include styrene,alpha-methyl styrene, various alkyl styrenes including p-methylstyrene,p-methoxy styrene, 1-vinyinaphthalene, 2-vinyl naphthalene, 4-vinyltoluene and the like. Styrene is preferred for copolymerization with1,3-butadiene alone or for terpolymerization with both 1,3-butadiene andisoprene.

The halogenated butyl elastomer may be used alone or in combination withother elastomers such as:

BR—polybutadiene

ABR—butadiene/C₁-C₄ alkyl acrylate copolymers

CR—polychloroprene

IR—polyisoprene

SBR—styreneibutadiene copolymers with styrene contents of 1 to 60,preferably 20 to 50 wt. %

IIR—isobutylene/isoprene copolymers

NBR—butadiene/acrylonitrile copolymers with acrylonitrile contents of 5to 60, preferably 10 to 40 wt. %

HNBR—partially hydrogenated or completely hydrogenated NBR

EPDM—ethylene/propylene/diene copolymers

The filler is composed of particles of a mineral, and examples includesilica, silicates, clay (such as bentonite), gypsum, alumina, titaniumdioxide, talc and the like, as well as mixtures thereof.

Further examples are:

-   -   highly disperse silicas, prepared e.g. by the precipitation of        silicate solutions or the flame hydrolysis of silicon halides,        with specific surface areas of 5 to 1000, preferably 20 to 400        m²/g (BET specific surface area), and with primary particle        sizes of 10 to 400 nm; the silicas can optionally also be        present as mixed oxides with other metal oxides such as those of        Al, Mg, Ca, Ba, Zn, Zr and Ti;    -   synthetic silicates, such as aluminum silicate and alkaline        earth metal silicate like    -   magnesium silicate or calcium silicate, with BET specific        surface areas of 20 to 400 m²/g and primary particle diameters        of 10 to 400 nm;    -   natural silicates, such as kaolin and other naturally occurring        silica;    -   glass fibres and glass fibre products (mafting, extrudates) or        glass microspheres;    -   metal oxides, such as zinc oxide, calcium oxide, magnesium oxide        and aluminium oxide;    -   metal carbonates, such as magnesium carbonate, calcium carbonate        and zinc carbonate;    -   metal hydroxides, e.g. aluminium hydroxide and magnesium        hydroxide; or combinations thereof.

These mineral particles have hydroxyl groups on their surface, renderingthem hydrophilic and oleophobic. This exacerbates the difficulty ofachieving good interaction between the filler particles and the butylelastomer. For many purposes, the preferred mineral is silica,especially silica prepared by the carbon dioxide precipitation of sodiumsilicate.

Dried amorphous silica particles suitable for use in accordance with theinvention have a mean agglomerate particle size in the range of from 1to 100 microns, preferably between 10 and 50 microns and most preferablybetween 10 and 25 microns. It is preferred that less than 10 percent byvolume of the agglomerate particles are below 5 microns or over 50microns in size. A suitable amorphous dried silica moreover has a BETsurface area, measured in accordance with DIN (Deutsche Industrie Norm)66131, of between 50 and 450 square meters per gram and a DBPabsorption, as measured in accordance with DIN 53601, of between 150 and400 grams per 100 grams of silica, and a drying loss, as measuredaccording to DIN ISO 787/11, of from 0 to 10 percent by weight. Suitablesilica fillers are available under the trademarks HiSil® 210, HiSil® 233and HiSil® 243 from PPG Industries Inc. Also suitable are Vulkasil® Sand Vulkasil® N, from Bayer AG.

Those mineral filler can may be used in combination with knownnon-mineral fillers, such as

-   -   carbon blacks; the carbon blacks to be used here are prepared by        the lamp black, furnace black or gas black process and have. BET        specific surface areas of 20 to 200 m²/g, e.g. SAF, ISAF, HAF,        FEF or GPF carbon blacks; or    -   rubber gels, especially those based on polybutadiene,        butadiene/styrene copolymers, butadiene/acrylonitrile copolymers        and polychloroprene.

Non-mineral fillers are not normally used as filler in the halobutylelastomer compositions of the invention, but in some embodiments theymay be present in an amount up to 40 phr. It is preferred that themineral filler should constitute at least 55% by weight of the totalamount of filler. If the halobutyl elastomer composition of theinvention is blended with another elastomeric composition, that othercomposition may contain mineral and/or non-mineral fillers.

The protected thiol modifier preferably comprises at least one siliconand one sulfur atom. Examples of suitable protected thiol modifiers aredisclosed in WO-99/09036-A1 which hereby is incorporated by referencewith regards to jurisdictions allowing for this feature.

Preferred are blocked mercaptosilanes selected from the group consistingof[[(ROC(═O))_(p)-(G)_(j)]_(k)-Y—S]_(r)-G-(SiX₃)_(s)  (1); and[(X₃Si)_(q)-G]_(a)-[Y—[S-G-SiX₃]_(b)]_(c)  (2)wherein

Y is a polyvalent species (Q)_(z)A(=E) selected from the groupconsisting of

—C(═NR)—; —SC(═NR)—; —SC(═O)—; —OC(═O)—; —S(═O)—; —S(═O)₂—;

—OS(═O)₂—;

—(NR)S(═O)₂—; —SS(═O)—; —OS(═O)—; —(NR)S(═O)—; —SS(═O)₂—;

(—S)₂P(═O)—;

—(—S)P(═O)—; —P(═O)(−)₂; (—S)₂P(═S)—; —(—S)P(═S)—; —P(═S)(−)₂;

(—NR)₂P(═O)—;

(—NR)(—S)P(═O)—; (—O)(—NR)P(═O)—; (—O)(—S)P(═O)—; (—O)₂P(═O)—;

—(—O)P(═O)—; —(—NR)P(═O)—; (—NR)₂P(═S)—; (—NR)(—S)P(═S)—;

(—O)(—NR)P(═S)—; (—O)(—S)P(═S)—; (—O),P(═S)—; —(—O)P(═S)—; and

—(—NR)P(═S)—;

each wherein the atom (A) attached to the unsaturated heteroatom (E) isattached to the sulfur, which in turn is linked via a group G to thesilicon atom;

each R is chosen independently from hydrogen, straight, cyclic orbranched alkyl that may or may not contain unsaturation, alkenyl groups,aryl groups, and aralkyl groups, with each R containing from 1 to 18carbon atoms;

each G is independently a monovalent or polyvalent group derived bysubstitution of alkyl, alkenyl, aryl or aralkyl wherein G can containfrom 1 to 18 carbon atoms, with the proviso that G is not such that thesilane would contain an alpha,beta-unsaturated carbonyl including acarbon-carbon double bond next to the thiocarbonyl group, and if G isunivalent, G can be a hydrogen atom;

X is independently a group selected from the group consisting of —Cl,—Br, RO—, RC(═O)O—, R₂C═NO—, R₂NO— or R₃N—, —R₃—(OSiR₃)_(t)(OsiR₃)wherein each R and G is as above and at least one X is not —R;

p is 0 to 5; r is 1 to 3; z is 0 to 2; q is 0 to 6; a is 0 to 7; b is 1to 3; j is 0 to 1, but it may be 0 only if p is 1, c is 1 to 6, t is 0to 5; s is 1 to 3; k is 1 to 2, with the provisos that

(A) if A is carbon, sulfur or sulfonyl, then (i) a+b=2 and (ii) k=1;

(B) if A is phosphorus, then a+b=3 unless both

(i) c>1 and (ii) b=1, in which case a=c+1; and

(C) if A is phosphorus, then k is 2.

Specific examples of protected thiol modifier comprise thioacetic acidS-trimethoxysilyl-methyl ester, thioacetic acid S-triethoxysilyl-methylester, thioacetic acid S-(2-trimethoxylsilyl-ethyl)ester, thioaceticacid S-(2-triethoxysilyl-ethyl)ester, thioacetic acidS-(3-trimethoxysilyl-propyl)ester, thioacetic acidS-(3-triethoxysilyl-propyl)ester, thiopropionic acidS-trimethoxylsilyl-methyl ester, thiopropionic acidS-triethoxylsilyl-methyl ester, thiopropionic acidS-(2-trimethoxylsilyl-ethyl)ester, thiopropionic acidS-(2-triethoxylsilyl-ethyl)ester, thiopropionic acidS-(3-trimethoxylsilyl-propyl)ester, thiopropionic acidS-(3-triethoxylsilyl-propyl)ester, thiobutyric acidS-trimethoxysilyl-methyl ester, thiobutyric acid S-triethoxysilyl-methylester, thiobutyric acid S-(2-trimethoxysilyl-ethyl)ester, thiobutyricacid S-(2-triethoxysilyl-ethyl)ester, thiobutyric acidS-(3-trimethoxysilyl-propyl)ester, thiobutyric acidS-(3-triethoxysilyl-propyl)ester, pentanethioic acidS-trimethoxysilyl-methyl ester, pentanethioic acidS-triethoxysilyl-methyl ester, pentanethioic acidS-(2-trimethoxysilyl-ethyl)ester, pentanethioic acidS-(2-triethoxysilyl-ethyl)ester, pentanethioic acidS-(3-trimethoxysilyl-propyl)ester, and pentanethioic acidS-(3-triethoxysilyl-propyl)ester. Preferred are pentanethioic acidS-(3-trimethoxysilyl-propyl)ester, and pentanethioic acidS-(3-triethoxysilyl-propyl)ester.

Preferably, the inventive compound comprises in the range of from 0.5 to10 phr of one or more protected thiol modifiers, more preferably in therange of from 1 to 5 phr.

It may be advantageous to add one or more silazane compounds to theinventive compound. These siliazane compound(s) can have one or moresilazane groups, e.g. disilazanes. Organic silazane compounds arepreferred. Examples include but are not limited to hexamethyldisilazane,heptamethyl-disilazane, 1,1,3,3-tetramethyldisilazane,1,3-bis(chloromethyl)tetramethyldisilazane,1,3-divinyl-1,1,3,3-tetramethyldisilazane, and1,3-diphenyltetramethyl-disilazane.

It may further be advantageous to further add additives which giveenhanced physical properties to the inventive compound such as hydroxyl-and amine-containing additives. Examples of hydroxyl- andamine-containing additives include proteins, aspartic acid,6-aminocaproic acid, diethanolamine and triethanolamine. Preferably, thehydroxyl- and amine-containing additive should contain a primary alcoholgroup and an amine group separated by methylene bridges, which may bebranched. Such compounds have the general formula HO-A-NH₂; wherein Arepresents a C₁ to C₂₀ alkylene group, which may be linear or branched.

More preferably, the number of methylene groups between the twofunctional groups should be in the range of from 1 to 4. Examples ofpreferred additives include monoethanolamine andN,N-dimethylaminoalcohol.

The amount of filler to be incorporated into the inventive halobutylrubber/elastomer compound can vary between wide limits. Typical amountsof filler range from 20 parts to 250 parts by weight, preferably from 30parts to 100 parts, more preferably from 40 to 80 parts per hundredparts of elastomer. The amount of the silazane compound is preferably inthe range of from 0.5 to 10 parts per hundred parts of elastomer,preferably of from 1 to 6, more preferably of from 2 to 5 parts perhundred parts of elastomer. The amount of hydroxyl- and amine-containingadditive used in conjunction with the silazane compound is typically inthe range of from 0.5 to 10 parts per hundred parts of elastomer,preferably of from 1 to 3 parts per hundred parts of elastomer.

Furthermore up to 40 parts of processing oil, preferably from 5 to 20parts, per hundred parts of elastomer, may be present. Further, alubricant, for example a fatty acid such as stearic acid, may be presentin an amount up to 3 parts by weight, more preferably in an amount up to2 parts by weight.

The halobutyl rubber(s)/elastomer(s), filler(s), protected thiolmodifier(s) and optional further additive(s) are mixed together,suitably at a temperature in the range of from 25 to 200° C. It ispreferred that the temperature in one of the mixing stages be greaterthan 60° C., and a temperature in the range of from 90 to 150° C. isparticularly preferred. Normally the mixing time does not exceed onehour; a time in the range from 2 to 30 minutes is usually adequate. Themixing is suitably carried out on a two-roll mill mixer, which providesgood dispersion of the filler within the elastomer. Mixing may also becarried out in a Banbury mixer, or in a Haake or Brabender miniatureinternal mixer. An extruder also provides good mixing, and has thefurther advantage that it permits shorter mixing times. It is alsopossible to carry out the mixing in two or more stages. Further, themixing can be carried out in different apparatuses, for example onestage may be carried out in an internal mixer and another in anextruder.

The enhanced interaction between the filler and the halobutyl elastomerresults in improved properties for the filled elastomer. These improvedproperties include higher tensile strength, higher abrasion resistance,lower permeability and better dynamic properties. These render thefilled elastomers particularly suitable for a number of applications,including, but not limited to, use in tire treads and tire sidewalls,tire innerliners, tank linings, hoses, rollers, conveyor belts, curingbladders, gas masks, pharmaceutical enclosures and gaskets.

In a preferred embodiment of the invention, bromobutyl elastomer, silicaparticles, protected thiol modifier(s) and, optionally, furtheradditives and/or, optionally, processing oil extender are mixed on atwo-roll mill at a nominal mill temperature of 25° C. The mixed compoundis then placed on a two-roll mill and mixed at a temperature above 60°C. It is preferred that the temperature of the mixing is not too high,and more preferably does not exceed 150° C., since higher temperaturesmay cause curing to proceed undesirably far and thus impede subsequentprocessing. The product of mixing these four ingredients at atemperature not exceeding 150° C. is a compound which has goodstress/strain properties and which can be readily processed further on awarm mill with the addition of curatives.

The filled halobutyl rubber compositions of the invention, and inparticular filled bromobutyl rubber compositions, find many uses, butmention is made particularly of use in tire tread compositions.Important features of a tire tread composition are that it shall havelow rolling resistance, good traction, particularly in the wet, and goodabrasion resistance so that it is resistant to wear. Compositions of theinvention display these desirable properties. Thus, an indicator oftraction is tan δ at 0° C., with a high tan δ at 0° C. correlating withgood traction. An indicator of rolling resistance is tan δ at 60° C.,with a low tan δ at 60° C. correlating with low rolling resistance.Rolling resistance is a measure of the resistance to forward movement ofthe tire, and low rolling resistance is desired to reduce fuelconsumption. Low values of loss modulus at 60° C. are also indicators oflow rolling resistance. As is demonstrated in the examples below,compositions of the invention display high tan δ at 0° C., low tan δ at60° C. and low loss modulus at 60° C.

The invention is further illustrated in the following examples.

EXAMPLES Description of Tests

Abrasion Resistance:

DIN 53-516 (60 grit Emery paper)

Physical Testing:

Stress-Strain measurements were determined at 23° C. on an Instron 4501according to ASTM 412 Method A. Samples for Stress-Strain measurementswere cut from a 2 mm macro sheet, cured for tc90+5 minutes, using Die C.Hardness values were determined with the use of a Shore A2 Testeraccording to ASTM 2240.

Dynamic Property Testing:

Dynamic testing (tan δ at 0° C. and 60° C., Loss modulus at 60° C.) werecarried out using the GABO. The GABO is a dynamic mechanical analyzerfor characterizing the properties of vulcanized elastomeric materials.The dynamic mechanical properties give a measure of traction with thebest traction usually obtained with high values of tan δ at 0° C. Lowvalues of tan δ at 60° C., and in particular, low loss moduli at 60° C.are indicators of low rolling resistance.

Cure Rheometry:

ASTM D 52-89 MDR2000E Rheometer at 1° arc and 1.7 Hz

Description of Ingredients:

BB2030—Bayer® Bromobutyl™ 2030—available from Bayer Inc.

RB301—Bayer® Butyl™ 301—non-halogenated Butyl available from Bayer Inc.

Hi-Sil® 233—silica—a product of PPG

NXT Silane—Pentanethioic acid S-(3-triethoxysilyl-propyl)ester a productof OSI

Maglite® D—magnesium oxide a product of CP Hall

HVA #2—m-phenyl-bis-maleimide—available from Dupont Canada Inc.

Stearic acid—available from H.M. Royal.

Sulfur NBS—available from Akron Rubber Development Laboratory Inc.

Zinc oxide—available from St. Lawrence Chem. Co. Ltd.

Examples 1-7

The effect of incorporation of protected thiol modifier(s) intohalogenated butyl elastomer/silica compounds was investigated via theformulation of several compounds of which NXT Silane was incorporated asthe protected thiol modifier. For comparison, a halogenated butylelastomer/silica compound (Example 1) with no silane and severalnon-halogenated butyl elastomer/silica compounds (Examples 3, 5 and 7)were also prepared as control compounds. The amount of ingredients usedis shown in Table 1.

Examples 1-7 were prepared with the use of two roll, 6×12 inch Milloperating with a roll temperature of 30° C. The compounds were preparedaccording to the following mixing sequence:

-   t=0 min: Add 1A+1B*-   t=2 min: Add 1C*-   t=3 min: Sweep-   t=4 min: Sweep-   t=5 min: Dump-   * as indicated in Table 1 in column “steps”

Each of these compounds was then heat treated (banding with a tight nipsefting) on a two roll, 6×12 in Mill operating with a roll temperatureof 100° C. for a total of 10 minutes. Following the heat treatment, thecuratives (2A) were added to the room temperature compounds with the useof a two roll 6×12 in Mill operating with a roll temperature of 30° C.The compounds were refined with six endwise passes.

TABLE 1 Test Formulations in phr (per hundred rubber). Amount in phrStep* Exp. 1 Exp. 2 Exp. 3 Exp. 4 Exp. 5 Exp. 6 Exp. 7 BB2030 1A 100 100100 100 RB301 1A 100 100 100 HI-SIL 233 1B 30 30 30 30 30 30 30 MAGLITED 1B 1 1 1 1 1 1 1 NXT SILANE 1B 2.4 2.4 2.4 2.4 2.4 2.4 HI-SIL 233 1C30 30 30 30 30 30 30 NXT SILANE 1C 2.4 2.4 2.4 2.4 2.4 2.4 HVA #2 2A 2 2STEARIC ACID 2A 1 1 1 SULFUR NBS 2A 0.5 0.5 0.5 1 1 ZINC OXIDE 2A 1.51.5 1.5 1 1 3 3 *Mixing step as referred to above

The physical properties of the compounds of Examples 1-7 wereinvestigated and are listed in Table 2.

TABLE 2 Test Compound Physical Properties. Exp. 1 Exp. 2 Exp. 3 Exp. 4Exp. 5 Exp. 6 Exp. 7 STRESS STRAIN (DUMBELLS) Dumbell Die C Die C Die CDie C Die C Die C Die C Test Temperature (° C.) 23 23 23 23 23 23 23Hardness Shore A2 (pts.) 67 57 47 63 46 55 50 Ultimate Tensile (MPa)7.56 17.02 1.94 17.07 0.375 18.25 4.03 Ultimate Elongation (%) 715 449DNB 283 DNB 450 DNB Stress @ 25 (MPa) 1.43 0.973 0.686 1.21 0.736 0.9680.716 Stress @ 50 (MPa) 1.36 1.27 0.705 1.87 0.687 1.26 0.781 Stress @100 (MPa) 1.35 1.93 0.695 3.8 0.571 1.99 0.816 Stress @ 200 (MPa) 1.755.06 0.682 10.62 0.451 5.54 0.932 Stress @ 300 (MPa) 2.57 10.45 0.7290.42 11.35 1.18 DIN ABRASION Abrasion Volume Loss (mm³) 418 209 TSTT 177TSTT 193 TSTT MDR CURE CHARACTERISTICS Frequency (Hz) 1.7 1.7 1.7 1.71.7 1.7 1.7 Test Temperature (° C.) 170 160 160 160 160 160 160 DegreeArc (°) 1 1 1 1 1 1 1 Test Duration (min) 60 60 60 60 60 60 60 TorqueRange (dN.m) 100 100 100 100 100 100 100 Chart No. 654 542 543 544 545546 547 MH (dN.m) 26.14 22.94 10.26 30.48 8.09 24.59 11.36 ML (dN.m)13.8 4.2 5.47 5.92 5.51 4.28 5.74 Delta MH-ML (dN.m) 12.34 18.74 4.7924.56 2.58 20.31 5.62 ts 1 (min) 0.3 0.96 4.32 0.84 29.34 0.96 4.8 ts 2(min) 0.36 1.5 11.22 1.56 48.24 1.56 10.38 t′ 10 (min) 0.27 1.41 1.732.11 9.11 1.54 2.86 t′ 25 (min) 0.47 3.18 5.48 7.23 20.67 3.46 6.87 t′50 (min) 4.14 8.41 14.85 16.62 34.92 8.93 16.44 t′ 90 (min) 37.47 31.4845.25 39.79 54.43 27.42 46.73 t′ 95 (min) 48.01 39.01 51.6 47.92 57.3132.98 52.85 DYNAMIC TESTING tan δ (0° C.) 0.621 0.631 tan δ (60° C.)0.163 0.135 E″ (60° C.) (MPa) 1.311 0.651 Note: TSTT = To Soft To Test.Compounds denoted as TSTT were deemed too soft to be tested by DIN53-516. DNB = Did Not Break. Compounds denoted as DNB possessed ultimateelongations which exceeded the upper limit of the Instron 4501,operating according to ASTM 412 Method A.

As can be seen from the data presented in Table 2, the physicalproperties of the compounds based on halogenated butyl (BB2030) aresignificantly superior to those measured for compounds based onnon-halogenated butyl (RB301). Regardless of which curative package wasemployed, the enhanced reactivity of compounds based on halogenatedbutyl (BB2030) compared to compounds based on non-halogenated butyl(RB301) allowed for the attainment of excellent physical properties inthe final compound. Specifically, compounds which were based on RB301(Examples 3, 5 and 7) possessed significantly poorer abrasion resistance(in fact these compounds were too soft to be tested) indexes compared totheir BB2030 analogues (Examples 2, 4 and 6). The significantly lowervalues of the modulus at 300% elongation for Examples 3, 5 and 7 c.f.Examples 2, 4 and 6 is yet a further indication of the poor degree offiller interaction (and thus physical reinforcement) present in theseformulations.

1. A filled halobutyl elastomer composition comprising at least onehalobutyl elastomer, at least one mineral filler, wherein the mineralfiller is selected from the group consisting of highly dispersed silicaprepared by the precipitation of silicate solutions or the flamehydrolysis of silicon halides, silicates, gypsum, alumina, titaniumdioxide, talc, and mixtures thereof, and at least one protected thiolmodifier.
 2. The filled halobutyl elastomer composition according toclaim 1 wherein the halobutyl elastomer is a Bromobutyl elastomer. 3.The filled halobutyl elastomer composition according to claim 1 whereinthe mineral filler is highly dispersed silica prepared by theprecipitation of silicate solutions or the flame hydrolysis of siliconhalides.
 4. The filled halobutyl elastomer composition according toclaim 1 wherein the at least one protected thiol modifier is a blockedmercaptosilane.
 5. The filled halobutyl elastomer composition accordingto claim 1 wherein the at least one protected thiol modifier is selectedfrom the group consisting of thioacetic acid S-trimethoxysilyl-methylester, thioacetic acid S-triethoxysilyl-methyl ester, thioacetic acidS-(2-trimethoxylsilyl-ethyl)ester, thioacetic acidS-(2-triethoxysilyl-ethyl)ester, thioacetic acidS-(3-trimethoxysilyl-propyl)ester, thioacetic acidS-(3-triethoxysilyl-propyl)ester, thiopropionic acidS-trimethoxylsilyl-methyl ester, thiopropionic acidS-triethoxylsilyl-methyl ester, thiopropionic acidS-(2-trimethoxylsilyl-ethyl)ester, thiopropionic acidS-(2-triethoxylsilyl-ethyl)ester, thiopropionic acidS-(3-trimethoxylsilyl-propyl)ester, thiopropionic acidS-(3-triethoxylsilyl-propyl)ester, thiobutyric acidS-trimethoxysilyl-methyl ester, thiobutyric acid S-triethoxysilyl-methylester, thiobutyric acid S-(2-trimethoxysilyl-ethyl)ester, thiobutyricacid S-(2-triethoxysilyl-ethyl)ester, thiobutyric acidS-(3-trimethoxysilyl-propyl)ester, thiobutyric acidS-(3-triethoxysilyl-propyl)ester, pentanethioic acidS-trimethoxysilyl-methyl ester, pentanethioic acidS-triethoxysilyl-methyl ester, pentanethioic acidS-(2-trimethoxysilyl-ethyl)ester, pentanethioic acidS-(2-triethoxysilyl-ethyl)ester, pentanethioic acidS-(3-trimethoxysilyl-propyl)ester, pentanethioic acidS-(3-triethoxysilyl-propyl)ester and mixtures thereof.
 6. A process forpreparing a filled halobutyl elastomer which comprises: admixing atleast one halobutyl elastomer, at least one mineral filler, wherein themineral filler is selected from the group consisting of highly dispersedsilica prepared by the precipitation of silicate solutions or the flamehydrolysis of silicon halides, silicates, gypsum, alumina, titaniumdioxide, talc, and mixtures thereof, at least one protected thiolmodifier and at least one cross-linking agent; and curing the resultingadmixture to make the filled halobutyl elastomer.
 7. A method forimproving the abrasion resistance of a filled, cured elastomercomposition comprising: providing at least one halogenated butylelastomer comprising at least one mineral filler, wherein the mineralfiller is selected from the group consisting of highly dispersed silicaprepared by the precipitation of silicate solutions or the flamehydrolysis of silicon halides, silicates, gypsum, alumina, titaniumdioxide, talc, and mixtures thereof; and admixing with said at least onehalogenated butyl elastomer at least one protected thiol modifier.